Pellicle, from the simple viewpoint that we often take as photographers, we consider white light to be a mix of some reddish, some greenish, and some bluish light. From that viewpoint, and considering your desire to remove (filter out) both some green and some red light, you would want to let the third color, blue, to come through unaffected. since mainly blue light is coming through, if you look through that filter, toward a white light), the filter appears bluish. But it sounds as if you already know this part.If I was wanting to absorb more of the green and some of the red spectra from a light source what colour filter would I use? I know that a blue appearing filter will remove more of the red and green, but what colour will a filter which removes some of the green as well appear?
Now, if you want to remove, for example, two units of green and only one unit of red (this is what you are asking, I think), here is one way to do it: first, use a blue filter with enough strength to remove both one unit of green and one unit of red. Now it remains only to remove one more unit of green. It turns out that such a filter, a green absorber, exists under the name of magenta. So your final filter pack would consist of the combination of blue filter and magenta filter. And if you hold it up to the light, and look through it, it has the appearance of a magenta-ish blue, or a bluish magenta, whatever you wish to call it.
Now, if you didn't know what magenta was, I'd describe it as a filter which blocks green, allowing red and blue to come through unscathed. So you could now see that my previous filter pack, blue plus magenta, is roughly equivalent to a double blue filter plus red filter, having a slightly reddish-blue appearance. Making any sense?
If you try to understand filters any deeper than these simple ideas, I think you need to look at spectral data. But for color printing, and using filters with only partial absorption, the ideas of red, green, and blue, combined with their complements of cyan, magenta, and yellow, work perfectly.
With regard to color printing, a rule I learned long, long time ago, which seems virtually infallible, is simply this, "Always do the wrong thing." If your print is too green, it seems like the wrong thing is to add green filtration. But do it anyway, it will work. Except, we don't normally use green filter, so you do the equivalent thing, which is to REMOVE magenta filtration. (I said it was equivalent, but actually it changes the exposure a bit).
A bit more comlicated example, per Bob-...'s "Too Cyan..." example: If your print is too cyan, you want to do the wrong thing, which is to add more cyan. However, conventionally, we don't adjust cyan; you want to do the equivalent thing, which is to remove red. However, we don't usually handle red filters, either, so you jump to the equivalent of removing both magenta and yellow. Once you work with this a bit, these equivalents will become second nature. In the meantime, you might want to consult that diagram, with three overlapping circles, labeled red, green, and blue. The little section opposite red is cyan, opposite green is magenta, and opposite blue is yellow.
Did I make this too long and complicated? If so, just remember, "always do the wrong thing."